Pressure sensitive adhesives are soft, permamently tacky polymers designed to adhere to a wide variety of substrates upon application of minimal pressure. These adhesives find wide use in such products as self-adhesive tapes and labels, stickers, wall covering and floor tiles. These adhesives have typically been supplied as polymeric solutions in organic solvents.
In recent years water borne pressure sensitive adhesives have been produced by the adhesives industry. These aqueous latex pressure sensitive adhesives compositions have been gaining wide favor due to their many advantages over organic solvent borne systems. These advantages include a reduction in air pollution and a reduction in fire hazard due to the substitution of water for organic solvent. There are also significant economic advantages as the price of organic solvents continues to increase.
Generally, aqueous latex pressure sensitive adhesives are produced by the use of surfactants in the production process. In a typical reaction a monomer mixture is added to an aqueous surfactant solution and polymerization initiated in a reactor.
These surfactant-based processes have led to the development of pressure sensitive adhesives having good adhesive properties, but these processes have also exhibited certain disadvantages. One problem is that surfactant based processes are complex and difficult to carry out because of the larger number of operations involved and the criticality of the properties of the products on the type and amount of surfactant used. Another disadvantage of surfactant based processes is their tendency to produce scrap; often greater than 0.5 weight percent of the polymer produced. Still another disadvantage is the additional cost of the required surfactants.
A process to produce a latex pressure sensitive adhesive having good adhesive characteristics, which avoids the necessity to employ surfactants, would be of great advantage.